What evidence do you have that merchants will standardize on incompatible sets of standards? Compatible standards benefit them.
Naturally compatible standards benefit them as a whole. But that does not mean someone is actually going to develop them. In fact, trade groups specifically asked the EU to create that cucumber standard.
It's also important note that such standards don't fall from heaven. They are the result of long consultations (often taking up to a decade) with all stakeholders. It's also not an EU-exclusive thing. I would be very surprised if there were no similar standards in the US.
A one-minute search has led me to this US government standard from which I can cherry-pick similar sentences:
https://www.ams.usda.gov/sites/default/files/media/Cucumber_...
> The maximum diameter of each cucumber shall be not more than 2-3/8 inches and the length of each cucumber shall be not less than 6 inches
> "Injury caused by scars" means scars which aggregate more than the area of a circle three-eighths inch in diameter on a cucumber 6 inches in length, or correspondingly greater areas of scars on larger cucumbers.
Implementation of that is (as far as I understand) voluntary but if you label your cucumbers "U.S. Fancy." you have to adhere to those standards. That's exactly the same as with the quoted EU regulation.
There is a reason why countries around the world develop such standards and it's not their love of bureaucracy.
Modern technological society is not a product of technology alone. We've had relatively intricate mechanical devices dating back to the Roman Coliseum, and before. Suits of armor had hasps, fasteners, catches, and wingnuts.
Modern society is a product of technology crossed with cheap flow of information crossed with interoperability standards. The suits of armor had wingnuts, but the wingnuts had individual faces carved onto them, because not even the left and right shoulder wingnuts were swappable. Common standards have built the shipping, transportation, telecommunications, and computing infrastructures that heavily define modern society today.